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ROLE OF IRON (II, III) HYDROXYCARBONATE GREEN RUST IN ARSENIC REMEDIATION USING ZEROVALENT IRON IN COLUMN TESTS
Su, C. AND R W. Puls*. ROLE OF IRON (II, III) HYDROXYCARBONATE GREEN RUST IN ARSENIC REMEDIATION USING ZEROVALENT IRON IN COLUMN TESTS. Presented at PRB RTDF Meeting, Niagara Falls, NY, October 15 - 16, 2003.
To inform the public.
We examined corrosion products of zerovalent iron (Peerless iron) that was used in three column tests for removing arsenic under dynamic flow conditions with and without added phosphate and silicate. Iron(II, III) hydroxycarbonate and magnetite were major iron corrosion products that were identified with X-ray diffraction. The column consisted of a 10.3-cm depth of 50 : 50 (w : w, Peerless iron : sand) in the middle and a 10.3-cm depth of a sediment from Elizabeth City, NC in both upper and lower portions of the 31-cm long glass column (2.5 cm in diameter) with three side sampling ports. The flow velocity (upflow mode) was maintained at 4.3 m d-1 during the three- to four- month experiments. The steady state As removal in the middle Peerless iron and sand mixture zone might be attributed to the continuous supply of corroded iron in the form of iron (II, III) hydroxycarbonate green rust and magnetite that served as the sorbents for both As(V) and As(III).There was evidence of oxidation of As(III) to form As(V) in the columns. Consistent with previous batch study findings, dissolved phosphate (0.5 or 1 mg P L-1) and silicate (10 or 20 mg Si L-1) showed strong inhibition for As(V) and As(III) (1 mg As(V) L-1 + 1 mg As(III) L-1 in 7 mM NaCl + 0.86 mM CaSO4) removal by Peerless iron in the column tests. The presence of combined phosphate and silicate resulted in earlier breakthrough (C = 0.5 C0) and earlier complete breakthrough of dissolved arsenic relative to absence of added phosphate and silicate in the bottom port effluent.